1,721,536 research outputs found
Numerical study of transonic buffet on supercritical airfoil with different boundary layer states
Full text linkAccurate numerical simulations of flow over airfoils play an increasingly
important role in the design of aircraft major components such as wings and turbo-
machinery blades. These lifting devices often operate in demanding aerodynamic
conditions for optimum performances, and may experience the presence of shock
waves in operating conditions. Shocks may become unsteady under specific
conditions, undergoing a large-scale, low-frequency periodic motion, which affects
the entire flow-field. This unsteady phenomenon, named transonic buffet, is the
subject of the present numerical investigation, with an oscillating shock over the
suction side of the airfoil.
In this study, a range of transonic Mach numbers and angles of incidence are
considered, but the bulk of the analysis is carried out for flow conditions at free-
stream Mach number M∞ = 0.7 and angle of incidence α = 7°, which show
well established buffet. Large-eddy simulations (LES) with natural and forced
transition carried out at chord Reynolds number Re = 3000000 clearly highlight
the effects of the incoming boundary-layer state on the shock oscillations. While a
laminar upstream boundary layer yields weak oscillations of the shock, a turbulent
incoming boundary layer yields significant buffet. The LES database has been used
to establish veracity (or not) of suggested buffet pathways, mainly based on the
alleged existence of an acoustic feedback loop. This mechanism is actually found
to consist of two separate patterns: coherent pressure disturbances convected from
the shock to the trailing edge, and acoustic waves scattered at the trailing edge,
feeding the shock motion. Additional exploration of the pressure side role in the
unsteadiness reveals that is has but marginal effect on the phenomenon.
Direct numerical simulations (DNS) at lower Reynolds number (Re = 300000)
suggest a reversal in the previously observed trend. In this case, a laminar incoming
boundary layer yields stronger buffet as compared to its turbulent counterpart,
highlighting strong dependence of the buffet phenomenon on the Reynolds number
when natural transition is considered. In order to passively control buffet, we
consider devices whose design is similar to large-eddy break-up devices (LEBU),
consisting of a thin circular-arc airfoil placed between shock and trailing edge, with
the main goal of: i) breaking the eddies originating at the shock, responsible for
the acoustic scattering at the trailing edge; ii) manipulating the acoustic field in the
aft part of the airfoil. RANS simulations show potential for this kind of device for
complete stabilization of buffet. On the other hand, DNS shows that the device is
able to curtail the buffet, but not to eliminate it. Additional tests are needed in
order to assess the effectiveness of the control device, whose practical impact might
be very larg
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Γ-convergence result for variational integrators of Lagrangians with quadratic growth
No full textFollowing the Γ-convergence approach introduced by Müller and Ortiz, the convergence of discrete dynamics for Lagrangians with quadratic behavior is established
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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